The present invention herein refers to a device for conveying fine powders through pipelines.
At the present state of the art there are various types of apparatus for transferring products in powder of various kinds from one container to another through special pipelines. In particular these types of apparatus are useful in painting plants that use paint in powder. In fact in such plants it is necessary to have an apparatus for the suction of paints in powder from any container whatsoever and for reconveying it to the spray painting guns.
Among the existing systems of conveying powder the Venturi-effect injectors can be mentioned. These injectors suck back the powder thanks to a jet of compressed air that is made to pass through a special convergent/divergent tube, and launch it along a conveyor tube using the same compressed air, often with the addition of supplementary conveying air. However, these systems present some problems, for example the consumption or the obstruction of the Venturi tubes, the inconstancy of the flow during prolonged use and the need for considerable maintenance. In addition the Venturi injectors require a high quantity of conveying air that then has to be discharged at the destination of the product in powder; this results in not being very convenient in various applications.
In addition to the Venturi injectors vacuum systems can also be mentioned. Such systems suck back the product in powder forming a vacuum in the conveying conduits. They have the problem of having to discharge the vacuum at the destination of the product; this makes it necessary to insert special devices that make the costs and complexity of the overall plant increase. In addition, the cleaning of the circuits of a vacuum system is rather difficult and problematic.
Recently the “volumetric” type of systems for the suction and reconveying of products in powder into pipelines have also been studied; nevertheless these systems use pistons with alternative movements and therefore, they are quite expensive.
Another system of conveying powders comprises a tubular chamber connected to the suction conduit by means of a first sleeve valve and to the delivery conduit by means of a second sleeve valve. Said chamber is positioned at a lower level than the tank from which the powders start, so as to allow the fall by gravity of the powders inside it. The chamber is fitted with an inlet of blowing air that enables the powder in it to be pushed into the delivery conduit. Such systems do not allow a continuous flow in output and have the disadvantage of having to be necessarily positioned at a lower level than the starting tank. To resolve the problem of the below-level positioning, the known technique of applying both a pressure source and a vacuum source alternatively to the hole was considered; in this manner it is possible to suck the powder into the chamber without relying only on the fall by gravity. In this embodiment, to find a solution between the need of suction and that of thrust of the powders, the hole is located in the chamber halfway between the inlet and the outlet. This causes strong disuniformity between the cycles of the pump and the quantity of powder injected at every cycle is variable and not easily controllable. To stabilize the flow in output from the device, it therefore became necessary to connect the two chambers in parallel with unsynchronized operating cycles. As a further disadvantage, the inlet valves of the two chambers are fitted with such a mechanical drive that when one of the two valves is open the other is closed. The two outlet valves are also fitted with a mechanical drive of this type. Such a device does not however permit the overlapping of the injection phases of the two chambers and thus does not allow a satisfactorily continuous flow of powder in output from the pump to be obtained.